Biluminescence via Fluorescence and Persistent Phosphorescence in Amorphous Organic Donor(D-4)-Acceptor(A) Conjugates and Application in Data Security Protection

Purely organic biluminescent materials are of great interest due to the involvement of both singlet and long-lived triplet emissions, which have been rarely reported in bioimaging and organic light-emitting diodes. We show two molecules 3,4,5,6-tetraphenyloxy-phthalonitrile (POP) and 3,4,5,6-tetrakis-p-tolyloxy-phthalonitrile (TOP), in which POP was found to exhibit fluorescence and persistent room temperature green phosphorescence (pRTGP) in the amorphous powder and crystal states. Both POP and TOP show aggregation-induced emission in a tetrahydrofuran-water mixture. We found in single-crystal X-ray analysis that intra- and intermolecular 1p(O)center dot center dot center dot pi interactions along with pi(C = C)center dot center dot center dot pi(C equivalent to N), hydrogen bond (H-B), and C-H center dot center dot center dot pi interactions induce a head-to-tail slipped-stack arrangement in POP. In addition, the X-ray structure of TOP with a slipped-stack arrangement induced by only pi(C=C)center dot center dot center dot pi(C equivalent to N) and H-B interactions shows dim afterglow only in crystals. These indicate that more noncovalent interactions found in POP may reinforce relatively efficient intersystem crossing that leads to pRTGP. Given the unique green afterglow feature in amorphous powder of POP, document security protection application is achievable.